Another interesting question, which I'd never really thought about.

There's a little bit in John Ellis' fascinating book, ' The Sharp End ' , viz : -

'Surprisingly, perhaps, (tank crews) were often very cold because the tank's engine was deemed more important than the men who manned it. In many models the engine was cooled by a fan in the turret and this wafted cold air, rain or snow indiscriminately over the actual motor and those in the bowels of the tank. The Matilda 1 was notorious for this as was the ubiquitous Sherman in which 'there was always a considerable downdraught going through the commander's cupola'. The Cromwell, too, suffered from this defect and more cold air was sucked through the driver's visor.
In the desert, however, this cold air could provide some sort of ventilation and air-conditioning. It was for this reason that although temperatures in stationary tanks often reached alarming levels, the starting of the engine brought speedy relief, and heat stroke, over which many fears had been expressed, was never a problem amongst armoured units'. ( 1990 edn, p.146 ).

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"Stand by to pull me out of the seat if I get hit" - Guy Gibson